Posts Tagged ‘hc11’

Back in the early 90s, I worked for TRW on a project to develop new technology for airbag sensors. The airbag sensor is the device in the car that decides whether or not to fire the airbag. Obviously, this is a pretty important, potentially life-saving decision. False negative … someone might die. False positive … someone might get unnecessarily injured by the airbag, not to mention the cost of reloading, which was about $2000.

The goal of the project was to migrate from mechanical sensors in the bumpers to electro-mechanical sensors under the gear shift to save wiring cost and improve reliability. An HC11 Motorola processor with a built-in accelerometer and A/D was used to measure the deceleration. The processor would evaluate the acceleration data and decide whether or not to fire the airbag.

Sounds simple enough. Since the integral of acceleration is velocity, add up the acceleration data and that is your change in velocity. The greater the change in velocity, the more likely a crash worth firing the airbag.

The guys in Michigan crashed up several different classes of cars to provide us with raw acceleration data files. Some of the raw data files had names like “30 MPH 50 lb Pig Left Front”. I can only imagine what they used to get this data . In any case, we had to run this data through our algorithm and make sure the airbags fired on real crashes but not on the others.

Easier said than done.

As it turned out, hitting a 50 lb. pig at 30 MPH is a pretty decelerating event. In the short 30 milliseconds required to make this decision, the algorithms had a hard time deciding what to do correctly.

It was only after 60ms or more that the algorithms started to reliably distinguish between a real crash and roadkill.

The critical issue was this … the timeframe was too short. There was no reliable way to differentiate all the possible “fire” scenarios from the “no fire” scenarios with just 30 ms worth of data. You just have to get more data. As it turned out, they redesigned the airbag to inflate faster, thereby allowing 60 ms to make a decision, which was just enough time.

It seems to me that we’re in the same boat with Global Warming.

We have a few decades of temperature data for an Earth that is 4.6 billion years old. Looking within those few decades, it looks like we might be heading for catastrophe.

Or, it might just be a normal temperature cycle.

Just as with the airbag sensor, we don’t have enough data to make a reliable decision one way or the other. And just as with the airbag, the cost of being wrong is great. False negative … we experience catastrophic climate shifts. False positive … we unnecessarily impose costs upon ourselves and developing countries that can cause social catastrophe.

Personally, I don’t know which is the right answer. And I don’t know how anyone else can know with certainty that they have the right answer. I wish that both sides in this discussion had a little more humility and they would acknowledge that they don’t know more than they do know. And that they could be wrong.